1) Field of the Invention
The present invention relates to a liquid crystal emulsion composition usable for providing a polymer dispersed type liquid crystal composite membrane through which a transmission of light can be controlled to a target value.
2) Description of the Related Art
Recently, a new type of liquid crystal composite membrane has been developed by utilizing a polymer dispersed type liquid crystal material, and this new type of liquid crystal composite membrane is useful as a film-shaped light shutter having a large area, or as a display means having a large area.
Where a polymer dispersed type liquid crystal layer prepared from a liquid crystal material having a positive dielectric anisotropy and a polymeric matrix having a refractive index substantially equal to an ordinary refractive index of the liquid crystal material is interposed between a pair of electrode plates, the resultant liquid crystal device can scatter rays of light irradiated thereon when an electric field is not applied thereto, and can allow a transmission of the light therethrough when the electric field is applied thereto.
Among various polymer dispersed types of liquid crystal materials, PCT International Publication No. WO 83/01016 discloses a Nematic Curvilinear Aligned Phase (NCAP) liquid crystal material; PCT Japanese Unexamined Patent Publication No. 60-252687 discloses a latex-entrapped liquid crystal material; PCT Japanese Publication No. 61-502128 discloses fine droplets of a liquid crystal material dispersed in an epoxy resin matrix, and Polymer Preprintings, Japan, Vol. 37, No. 8, 2450(1988) discloses a liquid crystal material composite membrane in which a liquid crystal material is formed into a network structure by a solvent casting method.
The formation of the polymer dispersed type liquid crystal composite membrane on a surface of a base plate can be carried out by (1) coating a surface of a base plate with a liquid crystal emulsion with a doctor blade coater or roll coater, and then drying the resultant coated liquid crystal emulsion layer on the base plate, or (2) interposing a layer comprising a mixture of a liquid crystal material with a prepolymer, between a pair of base plates, and then curing the resultant interposed mixture layer by a heating or light-irradiation procedure.
The above-mentioned methods are appropriate when forming a non-patterned polymer dispersed type liquid crystal composite membrane on a whole area of the base plate surface, but are disadvantageous in that, where a polymer dispersed type liquid crystal composite membrane must have a certain pattern, unnecessary portions of the non-patterned liquid crystal composite membrane must be removed in accordance with the required pattern.
If a printing method can be applied, the patterned liquid crystal composite membrane will be easily formed in accordance with the required pattern, on the base plate surface, and the removal of the portions of the liquid crystal composite membrane, which is not economical, can be avoided.
Nevertheless, when a conventional liquid crystal emulsion is printed in accordance with a required pattern, on a base plate surface, the resultant polymer dispersed type liquid crystal composite membrane is disadvantageous in that a number of bubbles are formed in the layer, and thus the smoothness of the resultant membrane surface is unsatisfactory.